The pseudobranchial circulation in Amia calva. 11]^ 



sections it was already partly enclosed in the cartilage of the skull, 

 a cartilaginous process of the postorbital process of the skull pro- 

 jecting backward along the lateral surface of the tissue. In the 

 specimen cut in horizontal sections this process of cartilage was not 

 developed, and the dorsal end of the diverticular tissue lay entirely 

 outside the cartilage of the skull. As the cartilage of the skull is 

 thus seen to grow backward instead of forward around the diverti- 

 culum, it seems improbable that the direct and active cause of the 

 occlusion of the spiracular cleft, in Amia, is the anterior translation 

 of the dorsal end of the hyomandibular , as Sagemehl (8) and 

 Wright conclude. 



The sense organ of the diverticulum of the pseudobranchial 

 chamber of Ä77iia is, as is well known, innervated by a branch of 

 the ramus oticus facialis. This would seem to indicate that the diverti- 

 culum is the homologue of the "auditory diverticulum of the spiracle in 

 Mustelus and other Selachians", and it is so considered by Wright, from 

 whom the above quotation is made. This auditory diverticulum of Se- 

 lachians has lately been considered by HoffiMAnn (4) as a remnant of 

 a pre-spiracular cleft. Nothing whatever, in Aniia^ in the development 

 of the cleft and diverticulum themselves, and wholly apart from any 

 significance that may be attached to their relation to the ramus oticus, 

 indicates, so far as I can see, that the diverticulum is such a structure. 



The pseudobranch of Amia lies, as is well known, in the antero- 

 lateral wall of the pseudobranchial cleft. In 12 mm larvae it is so 

 slightly developed that it is not as yet a determinate organ. It lies 

 close against the wall of the cleft, and its limits are so poorly defined 

 that it is difficult to recognise where the tissue of the organ begins 

 and the simple epithelium of the lining of the cleft ends. It lies 

 along the mesial surface of what may be described as a roll or bolster 

 of the tissues of the region, this bolster forming the antero-lateral 

 lip of the pseudobranchial cleft, and, projecting into it, nearly closing 

 it. The pseudobranchial chamber lies immediately dorsal to this 

 bolster. The bolster is much more strongly developed in older 

 larvae, while in the younger embryos examined it did not exist, the 

 entire cleft there being a simple wedge-shaped diverticulum of the 

 mouth cavity. 



The pseudobranch lies, in 12 mm larvae, throughout its entire 

 extent, anterior or antero-ventral to the dorsal portion of the hyo- 

 mandibular. The deep groove, or pocket, that connects the cleft with 

 the first branchial cleft extends backward internal to the hyomandi- 



